1. Field of the Invention
The present invention relates to novel azlactone compounds which are useful as intermediates for pharmaceutical agents, agrichemicals, and the like. The present invention further relates to methods of preparing such azlactone compounds.
2. Discussion of the Background
Azlactone compounds represented by the formula (II):
wherein P is a hydrogen atom, an alkyl group, an alkenyl group, an optionally substituted aryl group, an aralkyl group optionally having one or more substituent(s), or a haloalkyl group; and M is a hydrogen atom, sodium, potassium, or lithium, are useful as common starting materials for various heterocyclic derivatives such as pyrazoles, indoles, and the like, which are useful synthetic intermediates for pharmaceutical products, agrichemicals and the like, and various amino acid derivatives (see, e.g., Synlett, US, 1999, No. 1, pp. 120-122; and The Journal of Organic Chemistry, US, 2000, vol. 65, pp. 6138-6141), both of which are incorporated herein by reference in their entireties.
A known method for preparing azlactone compounds represented by formula (II) comprises reacting 4-ethoxymethylene-2-phenyl-5(4H)-oxazolone with an aqueous sodium hydroxide solution to give 4-hydroxymethylene-2-phenyl-5(4H)-oxazolone (International Journal of Peptide and Protein Research, Netherlands, 1995, vol. 45, pp. 266-271), which is incorporated by reference. However, a starting material compound in which the substituent at the 2-position of the azlactone ring is an aliphatic group (e.g., 4-ethoxymethylene-2-methyl-5(4H)-oxazolone, etc.) cannot be obtained in a high yield by this method, and the method is limited to compounds in which the substituent at the 2-position of the azlactone ring is an aromatic group such as a phenyl group and the like. Therefore, this method does not have high versatility.
A different method for the preparation of 4-hydroxymethylene-2-alkyl-2-oxazolin-5-one, which comprises reacting 4-(N,N-dimethylaminomethylene)-2-alkyl-2-oxazolin-5-one with sodium ethoxide in ethanol, is also known (Indian Journal of Chemistry, India, 2000, vol. 39B, pp. 688-693), which is incorporated herein by reference. However, when P is a methyl group or an ethyl group, this method also fails to provide an object compound in whihc M is a hydrogen atom. Although an azlactone compound in which P is a benzyl group and the like and M is a hydrogen atom can be obtained, a by-product such as a ring-opened product and the like occurs, and the method is not entirely satisfactory.
Thus, there remains a need for novel compounds of formula (II) described above. There also remains a need for improved methods for preparing compounds according to formula (II):